The present invention relates to a humidity detecting element comprising a resistor, which sensitively detects the humidity to vary the electric resistance. The present invention provides a humidity detecting resistor porcelain element which is useful as a detecting terminal for a humidity regulator and a humidity detecting apparatus using the element.
A metallic oxide is generally superior in moisture absorption, which is used to make the humidity detecting resistor. The metallic oxide humidity detecting elements are known for use in aluminum oxide thin films through the surface oxidation of aluminum sheet, colloid grains, glazed thin films mixed with glass components and partially with porcelain. However, the thin film or the colloid grain elements involve surface deterioration due to contamination or hysteresis. The glazed thin film element is stable with respect to atmospheric conditions and is restricted only to applications involving high humidity. The porcelain element is improved so as to be sensitive to a considerably lower humidity than the glazed element, but is restricted in control to a relative humidity of 20% or more. It is recognized that the glazed or the porcelain element is preferred in terms of response, thermal stability and atmosphere resistance as the humidity detecting element in the conventional embodiments. Since they are sintered at the high temperatures of 1,000.degree. C. or more, they are stable against the various atmospheres. For example, suppose that they are heated and cleaned at a time when the humidity detecting characteristics of the humidity detecting resistor have been removed due to the various gases (oil components), and they can be used semi-permanently. The heating system in the heating and cleaning operations is composed of a thermal radiation type wherein the humidity detecting resistor is heated through the radiated heat from a nearby-disposed resistance heating unit or is composed of a heat conduction type wherein a humidity detecting resistor is provided on the resistance heating unit through an insulating substratum to conduct the heat from the resistance heating through the insulating substratum to the humidity detecting resistor. However, in either of these cases, disadvantages such as an inferior thermal response, a longer response time, high consumption of power for the heating and cleaning operations, and more complicated construction were involved, whereby the use thereof was restricted. The present invention is created to provide a humidity detecting element free from the above-described conventional disadvantages.